I have the following code:
for x in "${array[#]}"
do
echo "$x"
done
The results are something like this (I sort these later in some cases):
1
2
3
4
5
Is there a way to print it as 1 2 3 4 5 instead? Without adding a newline every time?
Yes. Use the -n option:
echo -n "$x"
From help echo:
-n do not append a newline
This would strips off the last newline too, so if you want you can add a final newline after the loop:
for ...; do ...; done; echo
Note:
This is not portable among various implementations of echo builtin/external executable. The portable way would be to use printf instead:
printf '%s' "$x"
printf '%s\n' "${array[#]}" | sort | tr '\n' ' '
printf '%s\n' -- more robust than echo and you want the newlines here for sort's sake
"${array[#]}" -- quotes unnecessary for your particular array, but good practice as you don't generally want word-spliting and glob expansions there
You don't need a for loop to sort numbers from an array.
Use process substitution like this:
sort <(printf "%s\n" "${array[#]}")
To remove new lines, use:
sort <(printf "%s\n" "${array[#]}") | tr '\n' ' '
You can also do it this way:
array=(1 2 3 4 5)
echo "${array[#]}"
If, for whatever reason, -n doesn't fix this for you, you can also add \c to the end of the thing to be echo'd:
echo "$x\c"
Related
Suppose I have a Unix shell variable as below
variable=abc,def,ghij
I want to extract all the values (abc, def and ghij) using a for loop and pass each value into a procedure.
The script should allow extracting arbitrary number of comma-separated values from $variable.
Not messing with IFS
Not calling external command
variable=abc,def,ghij
for i in ${variable//,/ }
do
# call your procedure/other scripts here below
echo "$i"
done
Using bash string manipulation http://www.tldp.org/LDP/abs/html/string-manipulation.html
You can use the following script to dynamically traverse through your variable, no matter how many fields it has as long as it is only comma separated.
variable=abc,def,ghij
for i in $(echo $variable | sed "s/,/ /g")
do
# call your procedure/other scripts here below
echo "$i"
done
Instead of the echo "$i" call above, between the do and done inside the for loop, you can invoke your procedure proc "$i".
Update: The above snippet works if the value of variable does not contain spaces. If you have such a requirement, please use one of the solutions that can change IFS and then parse your variable.
If you set a different field separator, you can directly use a for loop:
IFS=","
for v in $variable
do
# things with "$v" ...
done
You can also store the values in an array and then loop through it as indicated in How do I split a string on a delimiter in Bash?:
IFS=, read -ra values <<< "$variable"
for v in "${values[#]}"
do
# things with "$v"
done
Test
$ variable="abc,def,ghij"
$ IFS=","
$ for v in $variable
> do
> echo "var is $v"
> done
var is abc
var is def
var is ghij
You can find a broader approach in this solution to How to iterate through a comma-separated list and execute a command for each entry.
Examples on the second approach:
$ IFS=, read -ra vals <<< "abc,def,ghij"
$ printf "%s\n" "${vals[#]}"
abc
def
ghij
$ for v in "${vals[#]}"; do echo "$v --"; done
abc --
def --
ghij --
I think syntactically this is cleaner and also passes shell-check linting
variable=abc,def,ghij
for i in ${variable//,/ }
do
# call your procedure/other scripts here below
echo "$i"
done
#/bin/bash
TESTSTR="abc,def,ghij"
for i in $(echo $TESTSTR | tr ',' '\n')
do
echo $i
done
I prefer to use tr instead of sed, becouse sed have problems with special chars like \r \n in some cases.
other solution is to set IFS to certain separator
Another solution not using IFS and still preserving the spaces:
$ var="a bc,def,ghij"
$ while read line; do echo line="$line"; done < <(echo "$var" | tr ',' '\n')
line=a bc
line=def
line=ghij
Here is an alternative tr based solution that doesn't use echo, expressed as a one-liner.
for v in $(tr ',' '\n' <<< "$var") ; do something_with "$v" ; done
It feels tidier without echo but that is just my personal preference.
The following solution:
doesn't need to mess with IFS
doesn't need helper variables (like i in a for-loop)
should be easily extensible to work for multiple separators (with a bracket expression like [:,] in the patterns)
really splits only on the specified separator(s) and not - like some other solutions presented here on e.g. spaces too.
is POSIX compatible
doesn't suffer from any subtle issues that might arise when bash’s nocasematch is on and a separator that has lower/upper case versions is used in a match like with ${parameter/pattern/string} or case
beware that:
it does however work on the variable itself and pop each element from it - if that is not desired, a helper variable is needed
it assumes var to be set and would fail if it's not and set -u is in effect
while true; do
x="${var%%,*}"
echo $x
#x is not really needed here, one can of course directly use "${var%%:*}"
if [ -z "${var##*,*}" ] && [ -n "${var}" ]; then
var="${var#*,}"
else
break
fi
done
Beware that separators that would be special characters in patterns (e.g. a literal *) would need to be quoted accordingly.
Here's my pure bash solution that doesn't change IFS, and can take in a custom regex delimiter.
loop_custom_delimited() {
local list=$1
local delimiter=$2
local item
if [[ $delimiter != ' ' ]]; then
list=$(echo $list | sed 's/ /'`echo -e "\010"`'/g' | sed -E "s/$delimiter/ /g")
fi
for item in $list; do
item=$(echo $item | sed 's/'`echo -e "\010"`'/ /g')
echo "$item"
done
}
Try this one.
#/bin/bash
testpid="abc,def,ghij"
count=`echo $testpid | grep -o ',' | wc -l` # this is not a good way
count=`expr $count + 1`
while [ $count -gt 0 ] ; do
echo $testpid | cut -d ',' -f $i
count=`expr $count - 1 `
done
I have the following at the moment:
for file in *
do
list="$list""$file "`cat $file | wc -l | sort -k1`$'\n'
done
echo "$list"
This is printing:
fileA 10
fileB 20
fileC 30
I would then like to cycle through $list and cut column 2 and perform calculations.
When I do:
for line in "$list"
do
noOfLinesInFile=`echo "$line" | cut -d\ -f2`
echo "$noOfLinesInFile"
done
It prints:
10
20
30
BUT, the for loop is only being entered once. In this example, it should be entering the loop 3 times.
Can someone please tell me what I should do here to achieve this?
If you quote the variable
for line in "$list"
there is only one word, so the loop is executed just once.
Without quotes, $line would be populated with any word found in the $list, which is not what you want, either, as it would process the values one by one, not lines.
You can set the $IFS variable to newline to split $list on newlines:
IFS=$'\n'
for line in $list ; do
...
done
Don't forget to reset IFS to the original value - either put the whole part into a subshell (if no variables should survive the loop)
(
IFS=$'\n'
for ...
)
or backup the value:
IFS_=$IFS
IFS=$'\n'
for ...
IFS=$IFS_
...
done
This is because list in shell are just defined using space as a separator.
# list="a b c"
# for i in $list; do echo $i; done
a
b
c
# for i in "$list"; do echo $i; done
a b c
in your first loop, you actually are not building a list in shell sens.
You should setting other than default separators either for the loop, in the append, or in the cut...
Use arrays instead:
#!/bin/bash
files=()
linecounts=()
for file in *; do
files+=("$file")
linecounts+=("$(wc -l < "$file")")
done
for i in "${!files[#]}" ;do
echo "${linecounts[i]}"
printf '%s %s\n' "${files[i]}" "${linecounts[i]}" ## Another form.
done
Although it can be done simpler as printf '%s\n' "${linecounts[#]}".
wc -l will only output one value, so you don't need to sort it:
for file in *; do
list+="$file "$( wc -l < "$file" )$'\n'
done
echo "$list"
Then, you can use a while loop to read the list line-by-line:
while read file nlines; do
echo $nlines
done <<< "$list"
That while loop is fragile if any filename has spaces. This is a bit more robust:
while read -a words; do
echo ${words[-1]}
done <<< "$list"
Hi I am reading in a line from a .csv file and using
echo $line
to print the cell contents of that record to the screen, however the commas are also printed i.e.
1,2,3,a,b,c
where I actually want
1 2 3 a b c
checking the echo man page there isn't an option to omit commas, so does anyone have a nifty bash trick to do this?
Use bash replacement:
$ echo "${line//,/ }"
1 2 3 a b c
Note the importance of double slash:
$ echo "${line/,/ }"
1 2,3,a,b,c
That is, single one would just replace the first occurrence.
For completeness, check other ways to do it:
$ sed 's/,/ /g' <<< "$line"
1 2 3 a b c
$ tr ',' ' ' <<< "$line"
1 2 3 a b c
$ awk '{gsub(",", " ")}1' <<< "$line"
1 2 3 a b c
If you need something more POSIX-compliant due to portability concerns, echo "$line" | tr ',' ' ' works too.
If you have to use the field values as separated values, can be useful to use the IFS built-in bash variable.
You can set it with "," value in order to specify the field separator for read command used to read from .csv file.
ORIG_IFS="$IFS"
IFS=","
while read f1 f2 f3 f4 f5 f6
do
echo "Follow fields of record as separated variables"
echo "f1: $f1"
echo "f2: $f2"
echo "f3: $f3"
echo "f4: $f4"
echo "f5: $f5"
echo "f6: $f6"
done < test.csv
IFS="$OLDIFS"
On this way you have one variable for each field of the line/record and you can use it as you prefer.
NOTE: to avoid unexpected behaviour, remember to set the original value to IFS variable
Hello I am trying to sort a set of numeric command line arguments and then echo them back out in reverse numeric order on the same line with a space between each. I have this loop:
for var in "$#"
do
echo -n "$var "
done | sort -rn
However when I added the -n to the echo the sort command stops working. I am trying to do this without using printf. Using the echo -n they do not sort and simply print in the order they were entered.
You can do it like this:
a=( $# )
b=( $(printf "%s\n" ${a[#]} | sort -rn) )
printf "%s\n" ${b[#]}
# b is reverse sorted nuemrically now
man sort would tell you:
sort - sort lines of text files
So you can transform the result into the desired format after sorting.
In order to achieve the desired result, you can say:
for var in "$#"
do
echo "$var"
done | sort -rn | paste -sd' '
Maybe that's because sort is "line-oriented", so you need every number on a separate line, which is not the case using -n with echo.
You could simply put the sorted numbers back in one line using sed, like that:
for var in "$#";
do
echo "$var ";
done | sort -rn | sed -e ':a;N;s/\n/ /;ba'
sort is used to sort multiple lines of text. Using the option -n of echo, you are printing everything in one line.
If you want the output to be sorted, you have to print it in multiple lines :
for var in "$#"
do
echo $var
done | sort -rn
If you want the result on only one line you could do :
echo $(for var in "$#"; do echo $var; done | sort -rn)
One trick is to play with the IFS:
IFS=$'\n'
set "$*"
IFS=$' \n'
set $(sort -rn <<< "$*")
echo $*
This is the same idea but easier to read with the join() function:
join() {
IFS=$1
shift
echo "$*"
}
join ' ' $(join $'\n' $* | sort -nr)
No loops required:
#!/bin/bash
sorted=( $(sort -rn < <(printf '%s\n' $#)) )
echo ${sorted[#]}
Sorting numbers in single line either comma, or space seperated, use the below
echo "12,12,3,55,567,23,6,9,35,423"|sed -e 's;[ |,];\n;g'|sort -n|xargs|sed -e 's; ;,;g'
if your output does not need comma, skip the sed after xargs
I have a variable like this:
words="这是一条狗。"
I want to make a for loop on each of the characters, one at a time, e.g. first character="这", then character="是", character="一", etc.
The only way I know is to output each character to separate line in a file, then use while read line, but this seems very inefficient.
How can I process each character in a string through a for loop?
You can use a C-style for loop:
foo=string
for (( i=0; i<${#foo}; i++ )); do
echo "${foo:$i:1}"
done
${#foo} expands to the length of foo. ${foo:$i:1} expands to the substring starting at position $i of length 1.
With sed on dash shell of LANG=en_US.UTF-8, I got the followings working right:
$ echo "你好嗎 新年好。全型句號" | sed -e 's/\(.\)/\1\n/g'
你
好
嗎
新
年
好
。
全
型
句
號
and
$ echo "Hello world" | sed -e 's/\(.\)/\1\n/g'
H
e
l
l
o
w
o
r
l
d
Thus, output can be looped with while read ... ; do ... ; done
edited for sample text translate into English:
"你好嗎 新年好。全型句號" is zh_TW.UTF-8 encoding for:
"你好嗎" = How are you[ doing]
" " = a normal space character
"新年好" = Happy new year
"。全型空格" = a double-byte-sized full-stop followed by text description
${#var} returns the length of var
${var:pos:N} returns N characters from pos onwards
Examples:
$ words="abc"
$ echo ${words:0:1}
a
$ echo ${words:1:1}
b
$ echo ${words:2:1}
c
so it is easy to iterate.
another way:
$ grep -o . <<< "abc"
a
b
c
or
$ grep -o . <<< "abc" | while read letter; do echo "my letter is $letter" ; done
my letter is a
my letter is b
my letter is c
I'm surprised no one has mentioned the obvious bash solution utilizing only while and read.
while read -n1 character; do
echo "$character"
done < <(echo -n "$words")
Note the use of echo -n to avoid the extraneous newline at the end. printf is another good option and may be more suitable for your particular needs. If you want to ignore whitespace then replace "$words" with "${words// /}".
Another option is fold. Please note however that it should never be fed into a for loop. Rather, use a while loop as follows:
while read char; do
echo "$char"
done < <(fold -w1 <<<"$words")
The primary benefit to using the external fold command (of the coreutils package) would be brevity. You can feed it's output to another command such as xargs (part of the findutils package) as follows:
fold -w1 <<<"$words" | xargs -I% -- echo %
You'll want to replace the echo command used in the example above with the command you'd like to run against each character. Note that xargs will discard whitespace by default. You can use -d '\n' to disable that behavior.
Internationalization
I just tested fold with some of the Asian characters and realized it doesn't have Unicode support. So while it is fine for ASCII needs, it won't work for everyone. In that case there are some alternatives.
I'd probably replace fold -w1 with an awk array:
awk 'BEGIN{FS=""} {for (i=1;i<=NF;i++) print $i}'
Or the grep command mentioned in another answer:
grep -o .
Performance
FYI, I benchmarked the 3 aforementioned options. The first two were fast, nearly tying, with the fold loop slightly faster than the while loop. Unsurprisingly xargs was the slowest... 75x slower.
Here is the (abbreviated) test code:
words=$(python -c 'from string import ascii_letters as l; print(l * 100)')
testrunner(){
for test in test_while_loop test_fold_loop test_fold_xargs test_awk_loop test_grep_loop; do
echo "$test"
(time for (( i=1; i<$((${1:-100} + 1)); i++ )); do "$test"; done >/dev/null) 2>&1 | sed '/^$/d'
echo
done
}
testrunner 100
Here are the results:
test_while_loop
real 0m5.821s
user 0m5.322s
sys 0m0.526s
test_fold_loop
real 0m6.051s
user 0m5.260s
sys 0m0.822s
test_fold_xargs
real 7m13.444s
user 0m24.531s
sys 6m44.704s
test_awk_loop
real 0m6.507s
user 0m5.858s
sys 0m0.788s
test_grep_loop
real 0m6.179s
user 0m5.409s
sys 0m0.921s
I believe there is still no ideal solution that would correctly preserve all whitespace characters and is fast enough, so I'll post my answer. Using ${foo:$i:1} works, but is very slow, which is especially noticeable with large strings, as I will show below.
My idea is an expansion of a method proposed by Six, which involves read -n1, with some changes to keep all characters and work correctly for any string:
while IFS='' read -r -d '' -n 1 char; do
# do something with $char
done < <(printf %s "$string")
How it works:
IFS='' - Redefining internal field separator to empty string prevents stripping of spaces and tabs. Doing it on a same line as read means that it will not affect other shell commands.
-r - Means "raw", which prevents read from treating \ at the end of the line as a special line concatenation character.
-d '' - Passing empty string as a delimiter prevents read from stripping newline characters. Actually means that null byte is used as a delimiter. -d '' is equal to -d $'\0'.
-n 1 - Means that one character at a time will be read.
printf %s "$string" - Using printf instead of echo -n is safer, because echo treats -n and -e as options. If you pass "-e" as a string, echo will not print anything.
< <(...) - Passing string to the loop using process substitution. If you use here-strings instead (done <<< "$string"), an extra newline character is appended at the end. Also, passing string through a pipe (printf %s "$string" | while ...) would make the loop run in a subshell, which means all variable operations are local within the loop.
Now, let's test the performance with a huge string.
I used the following file as a source:
https://www.kernel.org/doc/Documentation/kbuild/makefiles.txt
The following script was called through time command:
#!/bin/bash
# Saving contents of the file into a variable named `string'.
# This is for test purposes only. In real code, you should use
# `done < "filename"' construct if you wish to read from a file.
# Using `string="$(cat makefiles.txt)"' would strip trailing newlines.
IFS='' read -r -d '' string < makefiles.txt
while IFS='' read -r -d '' -n 1 char; do
# remake the string by adding one character at a time
new_string+="$char"
done < <(printf %s "$string")
# confirm that new string is identical to the original
diff -u makefiles.txt <(printf %s "$new_string")
And the result is:
$ time ./test.sh
real 0m1.161s
user 0m1.036s
sys 0m0.116s
As we can see, it is quite fast.
Next, I replaced the loop with one that uses parameter expansion:
for (( i=0 ; i<${#string}; i++ )); do
new_string+="${string:$i:1}"
done
The output shows exactly how bad the performance loss is:
$ time ./test.sh
real 2m38.540s
user 2m34.916s
sys 0m3.576s
The exact numbers may very on different systems, but the overall picture should be similar.
I've only tested this with ascii strings, but you could do something like:
while test -n "$words"; do
c=${words:0:1} # Get the first character
echo character is "'$c'"
words=${words:1} # trim the first character
done
It is also possible to split the string into a character array using fold and then iterate over this array:
for char in `echo "这是一条狗。" | fold -w1`; do
echo $char
done
The C style loop in #chepner's answer is in the shell function update_terminal_cwd, and the grep -o . solution is clever, but I was surprised not to see a solution using seq. Here's mine:
read word
for i in $(seq 1 ${#word}); do
echo "${word:i-1:1}"
done
#!/bin/bash
word=$(echo 'Your Message' |fold -w 1)
for letter in ${word} ; do echo "${letter} is a letter"; done
Here is the output:
Y is a letter
o is a letter
u is a letter
r is a letter
M is a letter
e is a letter
s is a letter
s is a letter
a is a letter
g is a letter
e is a letter
To iterate ASCII characters on a POSIX-compliant shell, you can avoid external tools by using the Parameter Expansions:
#!/bin/sh
str="Hello World!"
while [ ${#str} -gt 0 ]; do
next=${str#?}
echo "${str%$next}"
str=$next
done
or
str="Hello World!"
while [ -n "$str" ]; do
next=${str#?}
echo "${str%$next}"
str=$next
done
sed works with unicode
IFS=$'\n'
for z in $(sed 's/./&\n/g' <(printf '你好嗎')); do
echo hello: "$z"
done
outputs
hello: 你
hello: 好
hello: 嗎
Another approach, if you don't care about whitespace being ignored:
for char in $(sed -E s/'(.)'/'\1 '/g <<<"$your_string"); do
# Handle $char here
done
Another way is:
Characters="TESTING"
index=1
while [ $index -le ${#Characters} ]
do
echo ${Characters} | cut -c${index}-${index}
index=$(expr $index + 1)
done
fold and while read are great for the job as shown in some answers here. Contrary to those answers, I think it's much more intuitive to pipe in the order of execution:
echo "asdfg" | fold -w 1 | while read c; do
echo -n "$c "
done
Outputs: a s d f g
I share my solution:
read word
for char in $(grep -o . <<<"$word") ; do
echo $char
done
TEXT="hello world"
for i in {1..${#TEXT}}; do
echo ${TEXT[i]}
done
where {1..N} is an inclusive range
${#TEXT} is a number of letters in a string
${TEXT[i]} - you can get char from string like an item from an array